Java中的系统输入无法正常工作

Question

I'm trying to make a program that takes Ints and give me sum and I want to make it using regex. Input contains numbers, symbols and letters. For example when I write: java GiveMeSum 4 2 1 -5 or java GiveMeSum 4k "2 1 !-5 program should write 2 But it not only give me wrong answer, but also doesn't read all my input. When I write:

java GiveMeSum 4 2 1 -5

4 5 4 5 4 5 4 5

Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:864)
at java.util.Scanner.next(Scanner.java:1485)
at java.util.Scanner.nextInt(Scanner.java:2117)
at java.util.Scanner.nextInt(Scanner.java:2076)
at GiveMeSum.main(GiveMeSum.java:12)


public class GiveMeSum {

public static void main(String[] args) throws IOException {
    int sum = 0;
    Scanner sc = new Scanner(System.in).useDelimiter("(\\D|^-)");
    for ( int i = 0; i < args.length; i++) {
        sum += sc.nextInt();
    }
    System.out.println(sum);
}

}

Also there wasn't that exception. It's just showed up suddenly

Answer 1

This happens because you pass "4 2 1 -5" not as input but as arguments so they come into args parameter of the main method. To pass them as input wait till the app starts and enter them or use input stream redirection

Update (code for arguments processing)

How should I write it in java to take input as arguments then? Is there a specific easy way?

I'd say that using arguments for non-fixed number of input params is not so good idea. I'd still say that using input stream is the way to go - this is what it was designed for! Also your parsing requirements are a bit umbigious. Still here is my attempt

public class Main
{
    static OptionalInt parseOnlyInt(String s)
    {
        String digitsOnly = s.replaceAll("[^0-9]", "");
        if (digitsOnly.length() == 0)
            return OptionalInt.empty();
        else
            return OptionalInt.of(Integer.parseInt(digitsOnly));
    }

    public static void main(String[] args)
    {
        int sum = Arrays.stream(args)
                .map(Main::parseOnlyInt)
                // probably in Java 9 OptionalInt::stream would be better than next 2 lines
                // see https://bugs.openjdk.java.net/browse/JDK-8050820
                .filter(OptionalInt::isPresent)
                .mapToInt(OptionalInt::getAsInt)
                .sum(); 

        System.out.println(Arrays.toString(args));
        System.out.println(sum);    
    }
}

Or if you prefer the old (non-Java-8) way here it is

public static void main(String[] args)
{
    int sum = 0;
    for (int i = 0; i < args.length; i++)
    {
        String digitsOnly = args[i].replaceAll("[^0-9]", "");
        if (digitsOnly.length() != 0)
            sum += Integer.parseInt(digitsOnly);
    }
    System.out.println(Arrays.toString(args));
    System.out.println(sum);
}

Answer 2

System.in is the input stream. It only gets data after your program starts. Try looking at the args parameter to main. That is where data is put when it is passed in at invocation time.

Answer 3

A simple oneliner solution to take arguments and print sum

public static void main(String[] args) {
    int sum = Arrays.stream(args) // Create a stream from the array
            .mapToInt(Integer::parseInt) // Parse the strings as integers
            .sum(); // Sum
    System.out.println(sum);
}